New gas chromatography-mass spectrometry stable isotope techniques will be applied to the study of amino acid dynamics and whole body protein turnover in animals and man. Using highly precise methods developed in the principal investigator's laboratory we will measure labeled amino acid carbon and nitrogen transfer to the other amino acids, proteins, urea, ammonia, and exhaled carbon dioxide in both the whole animal and across organ and muscle beds. Such information should allow reasonably complete compartmentalization of amino acid transfer rates in vivo for the first time. Further additional use of the data will allow new insights into various established techniques for investigating the nutritional aspects of whole body protein turnover in adult man and in the neonate.